Could try smacking in a slightly oversize torx bit and se if that grips enough to remove.
Would be careful taking this route as the frame will be thin-walled in this area; potentially especially problematic if it's a placcy frame as they don't like impact / point loading..
You might try:
- Soak it in release agent overnight
- Get a bit of heat on it (again, not if the frame's placcy!)
-
Gently tap in a torx bit, subject to the above
- A reverse-helical extractor in the socket head, if you can find one that conveniently fits
- Drill and use the above deeper into the bolt shank; LH drill will probably help (all that's assuming you have room for the drill within the frame)
- If access allows cut a slot in the top with a cutting disc in a rotary tool
Good luck - stuff like this sucks!